Stable isotope compositions of precipitation in China

Transcription

1 Stable isotope compositions of precipitation in China Tellus Series B CHEMICAL AND PHYSICAL METEOROLOGY IF : 3.76 JianRong LIU, XianFang SONG, FuYuan GUO, Xiaomin SUN and LiHu YANG Reporter: Xu Jingzheng 2014/11/21

2 Outline Introduction Material and methods Results and conclusion The CHNIP stations isotopic characteristics. Seasonal variations Local MWL Correlations between δ 18 O and environmental variables (Temperature, meteorological and geographical) Conclusions 2

3 Introduction Stable isotopes are ideal tracers of water. The begin observations stable isotopic compositions of precipitation in China was in the mid-1980s (participated in the GNIP), but most were suspended after the mid-1990s. In 2004, CHNIP was established beacuse of the palaeoclimatologists. 3

4 Methods Material and methods Placed the equipment outside After each rainfall event, rainwater is collected and stored indoors below 4 o C. A pail was using collected snow, and after the event snow samples melt at room temperature. The end of the month, all collected water is mixed. Using a Finnigan MAT253 mass spectrometer and TC/EA method for 18 O and D content. 4

5 (NE:northeast NW:northwest TP:Tibetan NC:north China SC:south China) Fig. 1. The section of CHNIP and the section of GNIP 5

6 Results Fundamental isotopic characteristics of the CHNIP stations. The ranges of δd and δ 18 O NE > NW > TP > NC > SC(Time scale) The weighted δd and δ 18 O values in precipitation. SC > NW > NC > TP > NE (Space scale) 6

7 Linear δd-δ 18 O relationships based on all the CHINP from 2005 to (blue NE, yellow NC, green SC, red NW and purple TP) Triangle - spring Circle - summer Rectangle -autumn Diamond -winter) The weighted δd and δ 18 O values in precipitation. SC > NW > NC > TP > NE 7

8 Seasonal variations of the precipitation isotopes. I, II and III(3 < (δ s - δ w )< 12) major temperature contribution. Group IV main concentrated in the north of our country. The value of δ in SC winter are higher. Fig. 3. Distributions of δ s -δ w. δ s and δ w denote the un-weighted mean summer and winter. 8

9 δ 18 O Large, small and mediate seasonal fluctuations of δ 18 O are found in the northern (NW and NE), southern (SC) and NC regions, respectively. A V -shaped δ 18 O pattern is found at SC, while a reverse V -shaped pattern is found at NE and NW. The ranges of δd and δ 18 O NE > NW > TP > NC > SC 9

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11 LMWL (Local Meteoric Water Line) Based on the 928 groups of precipitation, CMWL is established as δd= 7.48*δ 18 O+1.01 LMWLs generally can be grouped into four types. Slope 8, most of these samples are distributed in SC. 7 < slope < 8, all of the NW and TP stations. The wider δ-ranges are caused by seasonal temperature variations and relatively low condensation temperature. Slope < 7 YT and DH stations, which located at the southeastern coast. The net evaporation is too high. Stations are located at the 30 o -45 o N continental inlands. Slope > 8, three SC stations are belong to this type. 11

12 The theoretical slope of LMWL (ST) can be calculated based on the condensation temperature, which is usually represented by the surface temperature (Criss, 1999): s T =(α 2-1)(1000+δD)/(α 18-1)(1000+δ 18 O) Where α 2 and α 18 are temperature dependent((friedman and O Neil, 1977; Criss, 1999): lnα 2 = (1/T) (1/T 2 ) lnα 18 = (1/T)+1137(1/T 2 ) The measured slopes are generally lower than the theoretical slope. Reason : Most of the precipitation has undergone raindrop evaporation effect. 12

13 Meteorological controls of δ 18 O In the SC, F v is the main control factor. δ C = α/α 0 * F v (α m -1) -1 (Dansgaatd,1961) F v is remaining fraction of the vapour phase.α α 0 α m refer to condensation t, initial t o and (t+t o )/2 The variation of δ 18 O show a strong dependence on precipitation. 13

14 In NC, correlation coefficients seem to be low. Except T and P, evaporation of the falling raindrops cause the high value of δ 18 O. In TP, the equations are formed by different variables, just like the NC. 14

15 In the NE and NW regions, T as a dominant control factor of δ 18 O. Except T, some other factors such as RH, Vp, Wd, and P are found to be critically influential for NW regions 15

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17 Fig. 5 Reconstruct time , based on Wulumuqi station. δ 18 O= T-0.146Wd 17

18 Geographical controls on δ 18 O CHNIP 1Latitude 20N and 50N. 2Longitude 80E and 140E. 3Altitudes range from less than 10 m on the eastern plain to over 3000 m on the TP. On the whole-country scale, δ 18 O is expressed as : δ 18 O = Lon-0.312Lat-0.002Alt 18

19 Conclusions The inner continental and coastal stations have larger or smaller δ-ranges, respectively, and the weight follow the SC > NW > NC > TP > NE. CMWL: δd=7.48δ 18 O+1.01, SC or TP, NW and NE samples upper or lower end of the line. Transformation is closely related to the stable isotope values and environmental variables. 19

20 The current work The Taihu Lake includes 32 sampling points that represent all the geographical and environment characteristics(fig. 1a). We divided Lake Taihu to seven sections: northern, northwestern, western, center, eastern, southwestern, and southeastern respectively(fig. 1b) Fig. 1a The Taihu lake Ecological zoning Fig. 1b sampling points Source: Lee et al.,

21 δd=8*δ 18 O+10 Fig 2. The correlation between δ 18 O and δd. GMWL : δd =8*δ 18 O+10 The value range of δd and δ 18 O generally follow the pattern: western > northwestern > southwestern > center > northern > southeastern > eastern, which indicates that the western lake section has the larger δ value range than the eastern lake section. 21

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24 Table 1. Descriptive statistics of isotope values of sampling points Lon Lat T δd(%) δ18o LMWL Station D-excess (o) (o) (oc) δdp(%) Min Max SD δ18op Min Max SD Slope Intercept R^2 Section 1(Northern) Section 2 (Northwestern) Section 3(Western) Section 4(Center)

25 Lon Lat T δd(%) δ18o LMWL Station D-excess (o) (o) (oc) δdp(%) Min Max SD δ18op Min Max SD Slope Intercept R^2 Section 5(Eastern) Section 6(Southwestern) Section 7(Southeastern)

26 The largest range of δd ( ) and δ 18 O ( ) are located at the sampling point 10 and 11,which is belong to western and southwestern section, respectively. The sampling point 3 have minimum standard deviation of δd( ), while point 31 have the minimum Std of δ 18 O( ). In total, the eastern section have the maximum of δd and δ 18 O, and the minimum of δd and δ 18 O occur at the northwestern section. 26

27 Except some points in the western region, the δ values of most points were lower than the GMWL. The maximum of d-excess was located at the western section of Lake Taihu and the minimum value was found in the southeastern section. The reasons are probably below: Stable isotopic values of input rivers and output rivers are not the same. The eastern lake is much shallower than the west. So under the same evaporation situation, the water in the east is more enriched than the west. Meteorology also plays a necessary role. 27

28 Thanks 28